- Review: What is a population?
- Biotic and abiotic factors affect population dynamics
- abundance, dispersion & age structure
- Population growth can be ‘modeled’
- tracking births & deaths
- Density matters
The big picture: The environment influences populations
Populations often described by their boundaries
Population density is dynamic
- May be possible to count all individuals
- large mammals, animals in small habitats
- More often impractical or impossible to count all individuals
- indirect estimates are needed
- dusk deer surverys in Biol 303
- Density is not static
- immigration:
- emigration:
- births & deaths
- motility
Local densities vary within a population
Population statistics change over time (demography)
- Cohorts:
- how many of one age-group survive to the next age level?
- when does reproduction occur?
- Girl power!
- only females produce offspring
- how many females give rise to new females`?
- how many years do females reproduce?
- Reproductive rates vs Survirorship
- key for conservation
Patterns of survivorship in natural populations
Populations grow fast when resources are abundant
Can we predict changes in population size?
- Start with ideal conditions:
- few individuals to start
- unlimited environment
- Population ↑ with births & immigration
- Population ↓ with deaths & emigration
- Balance of births & deaths at any given time
- per capita change (r) =
Elephants in Kruger National Park (Exponential Growth)
Resources rarely remain unlimited
- Carrying capacity (K):
- as population increases, resources diminish
- Resources that limit are vast
- food, shelter, safety, nesting sites
- Resource limitation causes birth rate to decline
- Logistic growth =
Trade offs exists between survival and reproduction
- Frequency of reproduction
- Number of offspring
- Investment into parental care
Combined there traits represents an organism’s life history
- Age at first reproduction
- How often reproduction occurs
- How many offspring are created
Trade offs exists between reproduction and survival
- Frequency of reproduction
- Number of offspring
- Investment into parental care
Combined there traits represents an organism’s life history
- Age at first reproduction
- How often reproduction occurs
- How many offspring are created
Trade offs exists between survival and reproduction
- Frequency of reproduction
- Number of offspring
- Investment into parental care
Combined these traits represents an organism’s life history
- Age at first reproduction
- How often reproduction occurs
- How many offspring are created
Trade-offs and Life Histories
Density in populations matter
- Why do populations stop growing?
- Density dependent =
- resources, predation
- disease, toxic waste
- Population density works as a negative feedback
Brainstorm: What factors are density independent?
Patterns in human population
Patterns in human population: Age structure
Patterns in human population: Density and carrying capacity
